1. Field of the Invention
The present invention relates to a method of forming relatively small or miniature electrical connector systems. More specifically, the present invention relates to a method of forming hermetically sealed but electrically conducting feedthroughs for devices, including biosensors and implantable devices. Electrically conducting feedthroughs are also described. Examples of implantable devices that can use such feedthroughs include the implantable component of a cochlear implant hearing prosthesis.
2. Related Art
The term ‘feedthrough’ as used herein refers to the provision of an electrically conducting path extending through an insulative member, from one side of the insulative member to another. The electrically conducting path may extend from the interior of a hermetically sealed container or housing on one side of the insulative member, to an external location outside the container or housing on the other side of the insulative member. Typically, a conductive path is provided by an electrically conductive pin, which is electrically insulated from the container or housing by an electrically insulating body surrounding the pin.
A feedthrough device can therefore allow one or more electrical connections to be made with electronic circuitry or components within an hermetically sealed container or housing, whilst protecting the circuitry or components from any damage or malfunction that may result from exposure to the surrounding environment.
There are many applications for feedthrough devices that provide an electrically conducting path through the wall of a housing or container whilst also sealing the electrical container or housing from its ambient environment. Historically, the first such devices were widely used in vacuum technology allowing for the transfer of signals between chambers of differing pressures. In such applications, the vacuum tubes had to be sealed because they could only operate under low-pressure conditions.
Over time, and with the advent of electrical devices capable of being implanted in body tissue to provide therapy to a patient, such as cardiac pacemakers, defibrillators and cochlear implants, the need to provide feedthrough devices with improved hermeticity has become increasingly important. As the environment of living tissue and body fluids is relatively corrosive and devices may contain materials which may be detrimental if exposed to the patient, a hermetic feedthrough device is used to provide a barrier between the electronic components of the device and the external corrosive environment of the human body. With implantable medical devices in particular, it is critically important that the hermetic seal of the device be physically rugged and long lasting. For this reason, stringent requirements are imposed on the hermeticity of an implanted device, typically requiring a seal that provides a leakage rate of less than 10−8 cc/sec.
Given this, feedthroughs used in medical implant applications, such as those used in pacemaker devices and cochlear implants, typically consist of a ceramic or glass bead that is bonded chemically at its perimeter through brazing or the use of oxides, and/or mechanically bonded through compression, to the walls of the sealed package. A suitable wire or other conductor passes through the centre of the bead, and this wire or conductor must also be sealed to the bead through chemical bonds and/or mechanical compression. Such feedthroughs are typically cylindrical and the wire(s) or conductor(s) mounted within the bead are centred or mounted in a uniform pattern, centrally within the bead.
Other materials and processes are known for making feedthroughs which rely, for example, on use of aluminium oxide ceramic and binders. These types of feedthroughs are widely used for cardiac implants and cochlear implants. One of the processes for making such a feedthrough consists of pre-drilling holes in a sintered ceramic plate and then forcing electrical conductive pins through the holes. While useful, this method is tedious and slow and does not necessarily guarantee a hermetic seal and generally results in unsatisfactory leakage rates on testing and low yields. A second method involves inserting the conductive pins into an unsintered (or ‘green’) ceramic plate and then curing the assembly by firing to achieve a hermetic seal. A major disadvantage of this last method is that, historically the manufacturing process has been performed by hand. Such a method of manufacture can lead to inaccuracies and be time consuming, expensive and labour intensive. Moreover, the feedthrough devices resulting from such a process do not necessarily have precisely positioned electrical conductors, with the position of the conductors being greatly dependent upon the process itself. Further, as the conductors are typically wires being of a general cylindrical shape and configuration, the size and shape of the conductor extending from the insulative material of the feedthrough is generally the same as the conductor embedded in the insulative material of the feedthrough.
As implantable devices continue to develop and become thinner, smaller and more electronically sophisticated, the requirements of the feedthrough have also increased. In cochlear implants, for example, where there is presently typically somewhere between 22-24 electrode leads, there is a need for 22-24 conductive pins passing through the feedthrough device. As the desire for more electrodes and smaller feedthroughs increases, the demands placed upon the design of the traditional feedthrough also increases. The problems in fabricating such a feedthrough device on such a large scale are therefore quite significant, especially when one considers the relatively high degree of labour intensity and specialisation of current fabricating methods.
While the above described prior art feedthrough devices and fabrication methods have proven successful, it is a relatively slow and labour intensive process to manufacture such devices. The method of manufacture of the feedthrough also presents limitations as to the construction of the feedthrough.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.